The present invention relates to the art of diagnostic imaging. It finds particular application in conjunction with nuclear or gamma cameras and will be described with particular reference thereto. It is to be appreciated, however, that the present invention will also find application in other non-invasive investigation techniques and imaging systems such as single photon planar imaging, whole body nuclear scans, positron emission tomography (PET) and other diagnostic modes.
In diagnostic nuclear imaging, one or more radiation detectors are mounted on a movable gantry to view an examination region which receives a subject therein. Typically, one or more radiopharmaceuticals or radioisotopes capable of generating emission radiation are injected into the subject. The radioisotope preferably travels to an organ of interest whose image is to be produced. The detectors scan the subject along a selected path or scanning trajectory and radiation events are detected on each detector.
Typically, the detector includes a scintillation crystal that is viewed by an array of photomultiplier tubes. The relative outputs of the photomultiplier tubes are processed and corrected, as is conventional in the art, to generate an output signal indicative of (1) a position coordinate on the detector head at which each radiation event is received, and (2) an energy of each event. The energy is used to differentiate between various types of radiation such as multiple emission radiation sources, stray and secondary emission radiation, transmission radiation, and to eliminate noise. A two-dimensional image representation is defined by the radiation data received at each coordinate. The radiation data is then reconstructed into an image representation of a region of interest.
Detecting radiation with two detector heads oppositely disposed from each other improves the resolution and data collection efficiency, particularly for whole body imaging. For other studies, particularly cardiac studies, it is advantageous to position the detector heads orthogonally to each other. This enables a complete 180 degree data set to be collected by rotating the pair of detector heads only 90 degrees relative to the subject. Still other gamma cameras have three heads placed at 120 degree intervals around the subject. Typically, the heads are movable radially toward and away from the patient and the three heads are rotatable, as a unit, around the patient. In each case, the detector face is placed as close as possible to the patient during a diagnostic scan for collimated imaging. The close proximity is necessary to minimize the loss in spatial resolution due to collimator blur.
Each of the foregoing systems has various advantages and disadvantages. The cost of a gamma camera system increases as additional detector heads are added. Systems having two opposed detector heads are particularly useful for whole-body imaging. Wide field of view detectors, which permit scanning of the entire width of the body, are preferably used in this application. Systems having two orthogonal detectors are commonly used for cardiac imaging. Because a wide field of view is not required in cardiac applications, smaller detectors are preferably used to allow the detectors to be placed as close as possible to the patient. Three detector head systems are often used in connection with high sensitivity brain and cardiac imaging. Although wide field of view detectors are desirable for body imaging, their physical size again limits performance in head imaging. Because the large detectors cannot be placed as close as possible to the patient's head, the system spatial resolution is compromised. The placement of the three detector heads also limits the utility of three detector systems in whole body and brain applications. Furthermore, as the detectors are moved, their associated field-of-view and resolution may change resulting in inaccurate collection of data and inaccurate reconstruction of images.
The present invention provides a new and improved diagnostic imaging system and method which overcomes the above-referenced problems and others.